In microwave and millimeter-wave automotive radar systems, low cost and high performance radar is required. The typical radar system includes an oscillator, a power divider, a power amplifier and a differential (or quadrature) hybrid combiner, using a single antenna to reduce the entire size. However, such a radar system is not very efficient since only half an output power flows to the antenna, while the other half flows to the ballast resistor of the hybrid. Alternately, if two separate transmitting and receiving antennas are utilized, the overall area occupied by the radar system is too large to embody a miniature radar system. In addition, the complete car radar system usually requires several transmitting and receiving paths with corresponding antennas to properly monitor the space from all sides of the car.
FIG. 1 illustrates a conventional automotive RADAR system 100 for transmitting and receiving radar signals. Radar system 100 comprises an oscillator 104 operable to supply a radio frequency (RF) signal 105 such as a millimeter wavelength signal. RADAR system 100 further comprises a power divider 110 which splits and drives the RF signal 105 to a power amplifier 120 and to a mixer (M) 160. The power amplifier 120 is used for amplifying and driving a radar transmission signal 125 into an antenna 150 and a ballast resistor 140, by way of a rat-race coupler or hybrid coupler 130. The mixer M 160 combines a received radar signal 155 from the antenna 150 by way of the coupler 130, with the original RF signal 105 by way of the divider 110, to provide an intermediate frequency (IF) signal 170. Thereafter, the IF signal 170 may be passed to a conventional RADAR detection system (not shown).
However, the conventional radar system 100 of FIG. 1 is not very efficient, since only half (50%) of the output power of the radar transmission signal 125 flows to the antenna 150, while the other half flows to the ballast resistor 140 on the hybrid coupler 130. Further, the system 100 requires a single ended RF signal 105 instead of a differential RF signal.